Direct measurement of intracellular pH changes in Xenopus eggs at fertilization and cleavage.
We have used Thomas-type recessed-tip pH-sensitive microelectrodes to measure the intracellular pH (pHi) in Xenopus eggs during both fertilization and ionophore activation. The average pHi in unfertilized eggs is 7.33 +/- 0.11 (SD; n = 21) with a resting membrane potential of -10.1 +/- 3.5 (SD; n = 38) mV. Within 2 min after the onset of the fertilization potential, there is a slight, transient pHi decrease of 0.03 +/- (SD, n = 8), followed by a distinct, permanent pHi increase of 0.31 +/- 0.11 (SD; n = 7) beginning approximately 10 min after the start of the fertilization potential and becoming complete approximately 1 h later. The pHi remains near this level of 7.67 +/- 0.13 (SD, n = 10) through at least 10 cleavage cycles, but it is possible to discern pHi oscillations with a mean amplitude of 0.03 +/- 0.02 (SD, n = 38). Eggs perfused for at least 2 h in Na+-free solution with 1 mM amiloride exhibited all of these pHi changes, so these changes do not require extracellular Na+. Similar cytoplasmic alkalinizations that accompany the activation of metabolism and the cell cycle in a wide variety of cell types are discussed.
D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002455:Cell Division; D005260:Female; D005306:Fertilization; D006863:Hydrogen-Ion Concentration; D008564:Membrane Potentials; D010063:Ovum / Q000502:physiology*; D012964:Sodium / Q000494:pharmacology; D014982:Xenopus laevis; D015053:Zygote / Q000502:physiology*
D000001:Calcimycin; D012964:Sodium